modeling a world made of cubes
As PeterT said.

Start by enabling the ANT Landscape addon. Open the user preferences Ctrl Alt U, got to the Addons tab, search for "Landscape". Click on the check mark on the right, if it is not already enabled.

Add a Landscape Shift A > Mesh > Landscape like the picture below.

Add a Remesh modifier to the object. Set the Mode: to Blocks. Increase the Octree Depth to get the resolution of the blocks you want.


Same Landscape mesh with only the Remesh modifier.


You can add the Remesh modifier to any mesh you do not have to start with the Landscape addon.